Some detection and ranging apparatuses may use a technology which combines a transmission sensor array including a plurality of transmission sensor elements and a reception sensor array including a plurality of reception sensor elements to effectively enlarge the aperture of the reception sensor array. Hereinafter, a radar apparatus will be described as a concrete example of a detection and ranging apparatus. The technology described above may be called holographic aperture synthesis, holograph, aperture synthesis, synthesis aperture or the like.
A radar apparatus using aperture synthesis radiates a probe signal modulated by an arbitrary method from a plurality of transmission sensor elements at time slots assigned to transmission sensors by time division multiplexing, for example. An echo signal caused by the reflection of the probe signal by a detection target is received by a plurality of reception sensor elements. The radar apparatus synthesizes the reception signals acquired at the time slots assigned to the transmission sensors. As a result, the radar apparatus can have an increased number of effective reception sensor elements and can detect an increased number of targets, thus improving the angular resolution. Hereinafter, a radar apparatus using aperture synthesis will be called an aperture synthesis radar. A sensor element and a sensor array are not distinguished from an antenna (element) and an array antenna, respectively. Reference may be made to Japanese Laid-open Patent Publication No. 2009-80024 and U.S. Pat. No. 7,196,656.